JPH05148568A - High density powder titanium alloy for sintering - Google Patents

Abstract

PURPOSE:To provide a high density powder titanium alloy for sintering capable of giving a high density product at a low cost and with high productivity. CONSTITUTION:The high density powder titanium alloy for sintering contains one kind or above two kind of element selected from a group consisting of Fe, Ni and Co and satisfies a condition of 0.5<=0.5Fe+Ni+0.6Co<=4 (wt.%) in the content and furthermore contains Mo of 0.5-4wt.% and balance Ti and inevitable impurities.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a titanium alloy for high density powder sintering which has excellent mechanical properties.

[0002]

BACKGROUND OF THE INVENTION Titanium alloys are lightweight and have high strength, and since they are excellent in corrosion resistance, they are expected to have a wide range of applications from industrial parts to consumer parts. In particular, it is being studied to apply the above properties to automobile parts. However, in the method of producing from ingot by machining or cold working, titanium having excellent mechanical properties can be obtained, but titanium is a difficult-to-process material, so that it is difficult to process, and the cost is high. In order to avoid such drawbacks, it has been attempted to apply a powder metallurgy technique in which elementary powders of a titanium alloy are mixed, shaped into a predetermined shape, and then fired in a vacuum to obtain a sintered body.
However, when the powder metallurgy technique is used, there is a problem that the mechanical properties of the product, particularly ductility and fatigue strength, are lower than those of the ingot material, because voids remain in the product.

In order to eliminate voids and increase the density after sintering, it has been attempted to carry out HIP (hot isostatic pressing) treatment after sintering (JESmugeresky et al. Powder).
Metallugy, 1981 and Hagiwara et al., Iron and Steel, 1986 (or Japanese Patent Publication No. 1-29864). If the HIP process is carried out, the density will certainly increase, and a powder sintered material with almost the same characteristics as the molten and forged material will be obtained. Especially the ductility (elongation, drawing) will be improved, but the manufacturing unit price will be extremely high. ..

Another method is to sinter at a temperature at which a liquid phase appears (see literature?). This is to make a liquid phase partially appear and try to fill the voids with the liquid phase. However, in this method, the heterogeneous phase produced by solidification of the partially liquid phase is generally brittle, and the resulting product is also brittle. That is, although the density can be increased, the mechanical properties are deteriorated. Further, the relationship between the sintering temperature and the mechanical properties is delicate, and there is a disadvantage that the characteristics change greatly with a slight temperature change.

Further, when a powder sintered titanium alloy is manufactured by the powder metallurgy technique, in addition to the problem that voids remain in the product, there is a problem that the productivity is low due to the sintering process. .. That is, since Ti is a refractory metal, the temperature for sintering is high and the time is long. Therefore, it is desired that low temperature and short time sintering be possible, but this cannot be achieved by the above two methods. Particularly, in the case of the latter method, since the firing is performed at a high temperature at which a liquid phase occurs, it is essentially impossible to satisfy such a requirement. As described above, a technique for obtaining a dense powder sintered body with few voids at low cost and with high productivity has not yet been established.
The present invention has been made in view of such circumstances,
An object of the present invention is to provide a high-density powder-sintered titanium alloy that can be densified at low cost and with good productivity.

[0006]

In order to solve the above-mentioned problems, the present invention contains one or more elements selected from the group consisting of Fe, Ni and Co,
And the content of these is 0.5 ≦ 0.5Fe + Ni + 0.6Co ≦ 4 (wt%)

Satisfying the condition of, and further 0.5 to 4% by weight
The present invention provides a titanium alloy for high-density powder sintering, characterized in that it contains Mo and the balance comprises Ti and unavoidable impurities.

Also, in this composition, by weight, 10% or less of Al, 15% or less of Nb, 15% or less of Ta, and 25%
V below, Ag below 10%, B below 5%, Be below 5%, Cr below 15%, Cu below 5%, Mn below 15%, Pb below 5%, Pb below 5%, below 5% One or two selected from Pd, Si of 5% or less, W of 10% or less, Sn of 15% or less, Zr of 10% or less, and O of 1% or less.
In the case of two or more kinds, they may be contained in a total amount of 30% or less.

The inventors of the present application have made various studies from the viewpoint of alloy composition in order to obtain a powder sintered body that is dense and has few pores at low cost and with good productivity. That is, a composition which can be densely sintered at a low temperature in a short time without a treatment such as HIP was studied. In order to densely sinter at a low temperature in a short time, it is necessary to have a high sintering rate, but for that reason, the diffusion rate in Ti is large, and it acts as an alloying element on Ti, and mechanical properties It was concluded that it is sufficient to add an appropriate amount of an element that does not adversely affect the.

As a result of investigating elements having a large diffusion rate in βTi, it was found that Fe, Ni and Co correspond to such elements. That is, the diffusion rate (diffusion coefficient) of these elements is 10 ^{−11 at} 950 ° C. Order (m
² .Sec ^-1 ), which is the self-diffusion rate of Ti 10
^-13 100 times larger than. Further, these elements contribute to the strength increase. However, if only such elements are used,
Due to the Kirkendall effect, pores are likely to be generated on the alloy component side, which may hinder densification.

In order to prevent such a situation, as a result of further study by the inventors of the present application, as a result of the above-mentioned elements having a large diffusion rate, addition of an element having a slow diffusion rate, that is, delaying sintering was added. I found that it was good.

As a result of investigating elements having a slow diffusion rate, Mo
Was found to correspond to such elements. Mo diffusion rate is 10 ^-10 Order of 1/10 of titanium
Is. Further, Mo is entirely dissolved in β titanium and functions as an alloying element. The present invention has been made based on such knowledge, and Ti, Fe, Ni, or Co,
And Mo are added in an appropriate amount.
Next, the reason for limiting the composition will be described.

Majima et al. (Powder and powder metallurgy, 19
87), there is a possibility that the densification may proceed to the vicinity of the composition that does not enter the solid-liquid coexistence region in the binary system phase diagram of Fe, Ni, Co and Ti. Further, from these binary phase diagrams, the composition that causes solid-liquid coexistence at 1200 ° C. is 1 for Fe.
It can be seen that 5%, Ni is 7%, and Co is 11%.
However, if these amounts are large, the ductility (toughness) will be reduced. Therefore, the upper limit when adding these alone is F
e8%, Ni4%, Co6.67%. Also,
If the amount is too small, the effect of densification cannot be obtained.
Therefore, the lower limit when adding these alone is Fe1
%, Ni 0.5%, Co 0.83%. However, these have similar effects, so it is necessary to specify the total amount. Therefore, these contents are specified so as to satisfy the following formula. 0.5 ≦ 0.5Fe + Ni + 0.6Co ≦ 4 (wt%)

Mo is an element having a slow diffusion rate in βTi as described above, and Fe, Ni, C having a high diffusion rate.
High density is achieved by coexisting with o. However, if the amount of Mo is less than 0.5%, the effect cannot be obtained, and if it exceeds 4.0%, the progress of the densification is delayed and the densification cannot be sufficiently achieved.

Al, Nb, Ta, V, Ag, B,
Be, Cr, Cu, Mn, Pb, Pd, Si, W, S
Since n, Zr, O, etc. are used as additive elements of the ingot and do not interfere with the sinterability intended in the present invention, they can be added in appropriate amounts in the same idea as in the ordinary ingot. Al and O are α-stabilizing elements, and when contained in the above range, they form a solid solution with Ti to remarkably increase the strength. Nb, Ta, and V are β-stabilizing elements, and all of them form a solid solution in Ti. Inclusion of these in the above range increases the strength.

Ag, B, Be, Cr, Cu, Mn, P
b, Pd, Si, and W are β-stabilizing elements, and cause eutectoid reaction with Ti. Inclusion of these in the above range also increases the strength. Sn and Zn are elements of stysy sodium, which form a solid solution in the α phase and β phase uniformly and improve the creep strength in addition to the static strength.

The titanium alloy for powder sintering of the present invention defined as above is manufactured by a method in which titanium powder and a pre-alloyed alloy powder are mixed, and the mixed powder is molded and sintered. Preferably. By adopting this method, the uniformity becomes good and the densification can be promoted. As such a method, Japanese Patent Publication No. 2-501
There is one described in Japanese Patent Laid-Open No. 72. this is,

(A) A prealloy consisting of two or more metals, having a mean particle size of 0.5 to 20 μm, using a crusher capable of imparting high energy to alloy forming particles which can be alloyed with titanium. Crush it to size,

(B) This and average particle size 40 to 177 μm
Of the titanium-based metal particles to form a powder mixture having a weight ratio of the titanium-based metal particles of 70 to 95% and the balance being the alloy-forming particles, and (c) the powder mixture having a theoretical value of The outline is that it is formed into a green compact having a density of 80 to 90%, and (d) the green compact is sintered at a temperature lower than a temperature at which a liquid phase is generated.

By using this method, the theoretical density of 9
A titanium alloy sintered body having a density of 9.0 to 99.8% can be obtained, and a density much higher than 94.5 to 96.5% of a titanium alloy prepared simply by mixing elementary powders. It will be possible. The mechanical properties are almost the same as those of the molten and forged titanium alloy. With the titanium alloy of the composition used conventionally, it was possible to sinter at a sintering temperature of 1260 ° C. for 4 hours by this method, but with the titanium alloy of the composition of the present invention, it is possible to sinter at a lower temperature in a shorter time. It will be possible.

[0021]

Embodiments of the present invention will be described below. (Example 1)

Raw material powders were blended so as to obtain a titanium alloy having the composition shown in Tables 1 and 2. Composition numbers 1 to 21 in Table 1 are examples within the scope of the present invention, and composition numbers 22 to 35 in Table 2 are comparative examples outside the range. In Tables 1 and 2, EQ1 is 0.5Fe + Ni +
Represents 0.6 Co.

Here, master alloy powders of alloy components corresponding to respective compositions were manufactured in advance. In this case, the master-alloy powder was manufactured as follows. First, the master alloys having the respective compositions were melted in an argon atmosphere arc melting furnace, solidified and then coarsely crushed to -100 mesh, and the diameter was about 3
About 10 kg of mm steel balls and 2 liters of Freon were placed in an attritor and crushed for about 60 minutes. Then, the pulverized powder was taken out from the attritor and dried. As a result of measuring the particle size of the master alloy powder particles thus produced with a laser micronizer, the average particle size was 3 to 5 μm.

These master alloy powders and pure titanium powder of -100 mesh (average particle size of about 75 μm) were mixed by a V blender so that each composition shown in Table 1 was obtained. Then, the mixed powder produced in this manner is filled in a steel mold, and the pressure is 5.0 tonf / cm ^2. 4 × 4 × 15
It was molded into a green compact of (mm). The density of the green compact was about 85% of the theoretical value.

The green compact of each composition molded in this way was set in a thermal expansion tester, and the ^{content was} adjusted to 10 ^-5 Torr order.
After evacuating, the mixture was heated to 1250 ° C at 10 ° C / min. Table 1 shows the temperature at which the density of the sintered body of each composition sintered by this heating becomes 99%. Since the test piece shrinks by almost 5% when it is sintered up to 99%, the point at which the test piece shrank 0.75 mm (5% of the original length of 15 mm) was defined as the density of 99%. As shown in Table 1, it was confirmed that a density of 99% can be obtained at a temperature as low as less than 1150 ° C. within the range of the present invention.

FIG. 1 shows the relationship between the value of 0.5Fe + Ni + 0.6Co and the temperature at which the density reaches 99%. FIG. 2 shows the relationship between the amount of Mo and the temperature at which the density reaches 99%. As is clear from these figures, the values of 0.5Fe + Ni + 0.6Co and Mo
It can be seen that the temperature at which the density reaches 99% decreases as the amount increases. And, such an effect is 0.
It can be seen that when the value of 5Fe + Ni + 0.6Co is 0.5% or more and the value of Mo is 0.5% or more, it becomes remarkable. Further, Table 1 also shows the addition amounts of Fe, Ni, and Co alone, but it can be seen that each element exhibits substantially equivalent effects. Composition numbers 19 to 21 are A as other alloy elements.
Although 1 and V were added, it was confirmed that the inclusion of these does not adversely affect the sinterability.

On the other hand, 0.5Fe + Ni + 0.6
Composition numbers 22, 23, 26, 28, 32, 34, 35 of comparative examples in which the value of Co or the content of Mo is less than 0.5%
In this case, as shown in Table 2, the temperature at which the density became 99% rapidly shifted to the high temperature side, and the temperature exceeded 1150 ° C. In addition, among these, the final density of composition number 22 was not 99%. In addition, Mo eye pay is 4.0
In the case of the composition numbers 24 and 33 that exceed 10%, the density is 9
The temperature of 9% exceeded 1150 ° C. (Example 2)

[0028] create a green compact of Example 1 and similar 4 × by mixing powder of each composition in Step 4 × 15 (mm), and set the thermal expansion tester therein 10 ^-5 Torr O After applying a vacuum of −10 ° C., the temperature was raised to 1150 ° C. at 10 ° C./min and the temperature was maintained for 4 hours. From the shrinkage amount of the test piece during this period,
The time required for the density to reach 99.5% of the theoretical density was obtained. Table 1 shows the values. In addition, since the test piece shrinks by about 5.2% when it is sintered up to 99.5%,
The point at which the test piece shrank 0.78 mm (5.2% of the original length of 15 mm) was defined as the density 99.5%. As shown in Table 1, within the range of the present invention, 99.
It was confirmed that a density of 5% was obtained.

FIG. 3 shows the relationship between the value of 0.5Fe + Ni + 0.6Co and the time for the density to reach 99.5%. FIG. 4 shows the relationship between the amount of Mo and the time for the density to reach 99.5%. As is clear from these figures, as the value of 0.5Fe + Ni + 0.6Co and the content of Mo increase, the time required for the density to reach 99.5% at 1150 ° C. decreases. In addition, such an effect is obtained by 0.5Fe +
It can be seen that when the value of Ni + 0.6Co is 0.5% or more and the content of Mo is 0.5% or more, it becomes remarkable.

On the other hand, 0.5Fe + Ni + 0.6
Composition numbers 22, 23, 26, 28, 30, 32, 3 of comparative examples in which the value of Co or the content of Mo is less than 0.5%
In the case of 4,35, the density is 99.5 as shown in Table 2.
%, The time to reach 100% suddenly shifted to the super-time side, and the time exceeded 160 minutes. Also, of these, composition number 22
And 30, the density did not reach 99.5% in 4 hours. Further, in the case of the composition numbers 24 and 33 in which the Mo content exceeds 4.0%, the time for the density to reach 99.5% exceeded 160 minutes. (Example 3)

After molding a green compact of 13 × 13 × 69 (mm) from the mixed powder of each composition by the same procedure as in Example 1,
Sintering was performed for 4 hours at 1250 ° C. in a vacuum of 10 ⁻⁵ Torr order. Tensile test pieces having a parallel portion with a diameter of 6.25 mm and a gauge length of 25 mm were produced from the sintered bodies of the respective compositions thus produced, and the tensile test was carried out at room temperature. Table 1,
Table 2 also shows the values of tensile strength and elongation at break.
As is apparent from Table 1, for compositions within the scope of the present invention,
It was confirmed that both tensile strength and elongation at break show sufficient values.

FIG. 5 shows the relationship between the value of 0.5Fe + Ni + 0.6Co and the elongation at break. FIG. 6 shows the relationship between the amount of Mo and the elongation at break. As is clear from these figures, the elongation at break is 0.5Fe + N
The value of i + 0.6Co and the content of Mo tend to decrease as the content of Mo increases, and one of these values is 4.0.
It can be seen that elongation exceeds abruptly when it exceeds%.

That is, as shown in Table 2, 0.5Fe
Composition numbers 24, 25, 27, 29, 3 of Comparative Examples in which the value of + Ni + 0.6Co or the content of Mo exceeds 4.0%
It was confirmed that 1,33 has an elongation at break of 3% or less, which is extremely low, and the addition of more than 4.0% is not preferable. It is considered that this is because the excessive addition of Fe, Ni, Co, and Mo promotes the formation of intermetallic compounds and significantly reduces the toughness.

It is confirmed that the composition numbers 19 to 21 to which Al and V are added as alloy elements have high tensile strength. For example, comparing alloy numbers 1 and 19, the tensile strength is 46 kgf / cm ² Is also rising. That is, A
It was confirmed that the strength was increased by adding 1 and V.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

According to the present invention, there is provided a high-density powder-sintered titanium alloy which can be densified at low cost and with good productivity.

[Brief description of drawings]

FIG. 1 shows a value of 0.5Fe + Ni + 0.6Co and a density of 9
The figure which shows the relationship with the temperature which reaches 9%.

FIG. 2 is a diagram showing the relationship between the amount of Mo and the temperature at which the density reaches 99%.

FIG. 3 shows a value of 0.5Fe + Ni + 0.6Co and a density of 9
The figure which shows the relationship with the time required to reach 9.5%.

FIG. 4 is a diagram showing the relationship between the amount of Mo and the time required for the density to reach 99.5%.

FIG. 5 is a diagram showing the relationship between the value of 0.5Fe + Ni + 0.6Co and elongation.

FIG. 6 is a diagram showing the relationship between Mo content and elongation.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuji Ito Marunouchi 1-2-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Steel Pipe Co., Ltd.

Claims (2)

[Claims] 1. An element containing one or more elements selected from the group consisting of Fe, Ni, and Co, and the content of these elements is 0.5 ≦ 0.5Fe + Ni + 0.6Co ≦ 4 (weight %), Further containing 0.5 to 4% by weight of Mo, and the balance being Ti and inevitable impurities, a titanium alloy for high-density powder sintering. 2. In% by weight, 10% or less of Al, 15% or less of Nb, 15% or less of Ta, 25% or less of V, 10%
Ag below, B below 5%, Be below 5%, Cr below 15%, Cu below 5%, Mn below 15%, Pb below 5%, Pd below 5%, Pd below 5%, Si, W of 10% or less, Sn of 15% or less, Zr of 10% or less, and 1
% Or less, and further contains one or more kinds selected from O in a range of 30% or less in total in the case of two or more kinds. Titanium alloy for powder sintering.